Jeweler Help!

Hey all... so I've been engaged for about a year.... my mom actually helped my fiance pay for my current engagement ring since money is always so tight, this was after offering a ring from my grandma (it was set way to high... it was more of a cocktail ring, so I didnt take it at the time) my grandmother passed away this year and 8 weeks later my mother passed away. Since they will not be with me when i get married, I wanted to incorporate both rings together to create a new engagement ring having the diamonds from my current ring and the diamonds from my grandmother's ring. Anyone know of any good/reliable jewelers who could help?? It is really important to me that these diamonds are not swapped out for other ones, not so much for value reasons but for sentimental reasons. I am nervous but its something i have discussed with my fiance and family and would be a constant reminder of the greatest women ever in my life. Please help!